Various constructions of rack and pinion type rotary actuators are known. Such rotary actuators are available in a wide range of sizes and torque outputs. They may be powered by either air or hydraulic fluid under pressure. Various rack and pinion type rotary actuators of different construction and in a range of sizes are described, for example, in a brochure entitled "FLO-TORK Rotary Actuators", published by FLO-TORK, Inc., Orrville, Ohio, 1984 (20 pages). On page 7 of this brochure is illustrated a two-rack hydraulic rotary actuator having four floating pistons, (one at each end of each rack), two one-piece racks, rack bearings, and a one-piece pinion and output shaft which is driven by the racks. The racks and rack bearings in this rotary actuator have flat surfaces which are in contact with each other, so that a certain amount of sliding contact between each rack and its rack bearing can take place. Such movement results in a certain degree of misalignment of the rack in its cylinder, and can even result in tilting of the pistons.
Other references describing rack and pinion type rotary actuators include, for example, Steiner, U.S. Pat. No. 2,844,128, Meyer et al, U.S. Pat. No. 3,156,160, and Carr, U.S. Pat. Nos. 3,213,760 and 3,246,581.